Pressure actuated flow control valve

ABSTRACT

A pressure actuated flow control valve for an infusion catheter permits gravity flow of a liquid through the catheter and into a patient while resisting back flow of blood from the patient and into the catheter. The valve has a hemispherical body with an outstanding circumferential flange and a normally closed, diametric slit. The slit is longer on the convex outer surface than on the concave inner surface. Dome thickness diminishes in the area adjacent the slit, reducing total apical deflection upon collapse of the slit toward the concave surface. An inner orthogonal rib biases the slit closed. Upon application of a predetermined pressure, the slit opens toward the concave surface to permit forward fluid flow. At lower pressures, the slit closes to check fluid flow. Greater reverse pressure is required to collapse the slit toward the concave surface to permit reverse fluid flow.

CROSS REFERENCE(S)

This application is a continuation-in-part application of U.S.application Ser. No. 10/304,833 filed Nov. 26, 2002

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention is broadly concerned with a control valve for amedical fluid infusion device. More particularly, it is concerned with apositive pressure actuated flow control valve that permits flow of aliquid from a reservoir, through a cannula and into a patient, whileresisting reflux.

2. Background Art

Medical infusion therapy employs peripheral and central intravasculardevices such as venous and arterial catheters as well as peripherallyinserted central venous catheters to deliver fluids, blood products, andpharmaceuticals, including antibiotics and biologics as well asparenteral nutrition. Intravascular devices may also be coupled withpressure monitoring systems.

Regardless of the location of the insertion site of the catheter or theplacement of its terminus, intravascular devices, and central venouscatheters (CVCs) in particular, are subject to retrograde blood flowinto the catheter lumen whenever the pressure in the patient's vascularsystem exceeds resistance at the supply end of the catheter. This mayoccur, for example, when fluid pressure drops because a gravity supplysource is empty, when an injection port is opened by removal of asyringe, or when a stopcock is opened.

Retrograde blood flow is known to contribute to complications such ascatheter-related septicemia, venous thrombosis, superior vena cavasyndrome, pulmonary embolism and phlebitis. Thrombus formation may causepartial or complete occlusion of the catheter. Partial occlusion resultsin impaired sampling and fluid administration. Complete occlusion causesthe catheter to lose patency, necessitating removal and replacement,so-called “unscheduled restarts”.

Catheter reflux induced thrombosis is not merely a mechanicalcomplication, since it appears to be a major contributor to catheterrelated bloodstream infections associated with the use of long termcatheters. Such infections are associated with increased morbidity andmortality as well as increased health care costs associated withextended hospitalization.

Attempts have been made to develop improved intravascular devices inorder to address the mechanical and infectious complications previouslydescribed. Peripherally inserted central venous catheters (PICC) areknown to reduce the incidence of thrombosis and phlebitis as well ascommonly reported central catheter-related infections. However, PICCdevices are not suitable for all applications, particularly where thesolution to be administered has high osmolarity or may be a pH irritant.And patients with PICC infusion still experience thrombus formation andphlebitis at statistically significant levels.

Guidewire assisted exchange has also been employed to achieve a lowerrate of mechanical complications following insertion of replacementcatheters. However, patients may experience bleeding, hydrothorax andsubsequent catheter related infections.

In-line filters have also been employed to reduce infusion-relatedphlebitis. However, they have not been found to prevent intravasculardevice-related infections. And use of such filters is not regarded asmechanically favorable, since solution filtration may be accomplishedmore efficiently prior to infusion and the filters themselves aresubject to blockage.

Impregnated catheters and needle-free devices have also been employed.Although they have not yet been thoroughly evaluated, antimicrobialcoated or impregnated catheters appear to be more effective for centralvenous use than for peripheral use. There are concerns, however, thatthey may foster development of resistant bloodstream pathogens.Needle-free infusion systems also have not yet been fully studied,although one investigation has shown survival of skin flora inneedleless infusion systems.

There have also been attempts to develop methods of using conventionalintravascular devices in order to prevent catheter-related thrombusformation and to maintain catheter patency. Turbulent positive pressureflushing with anticoagulant heparin solution, use of thrombolytic agentssuch as urokinase, streptokinase and t-Pa, and prophylactic warfarinadministration have all been employed.

However, some in vitro studies have suggested that heparin flushsolutions may serve to enhance growth of Coagulase-negativestaphylococci (CoNS). The United States Public Health Service, Centersfor Disease Control and Prevention (CDC) has cited CoNS as “the primarypathogen causing catheter-related infections. It has recommendedclinical trials to evaluate the practice of flushing with anticoagulantsolutions to prevent catheter-related infections. The CDC has also citedan association between use of low dose heparin and thrombocytopenia andthromboembolic and hemorrhagic complications.

All of the preventive methods that are currently available appear tocontribute in some manner to general health care delivery problems, suchas delay, increased requirements for nursing care, pharmaceutical andsupply costs, increased patient risk and discomfort.

Accordingly, there is a need for an improved intravascular device thatwill resist retrograde blood flow and thereby reduce rates of thrombusformation, catheter-related blood stream infection, and unscheduledrestarts and thereby extend catheter indwelling times.

SUMMARY OF THE INVENTION

The present invention is directed to a pressure actuated flow controlvalve for an infusion catheter which permits gravity flow of a liquidthrough the catheter and into a patient while resisting back flow ofblood from the patient and into the catheter. The valve is a flexibleunitary body having a central wall that defines a fluid passagewayportal. The valve includes a central wall, which in one embodiment is ahemispherical dome-shaped body having concave inner and convex outersurfaces. However, dome-shaped as utilized herein does not necessarilymean that the concave inner and the convex outer surfaces are sphericalor substantially spherical. Dome-shaped simply refers to the concave andconvex nature of the surfaces in that they have an arcuate cross-sectionbut not necessarily circular. A normally closed opening communicatesbetween the surfaces. The opening, normally identified as a slit, canextend along a diameter of the central wall and is configured so that itis longer on the convex outer surface than on the concave inner surface.The term slit is utilized to refer to a narrow elongated opening or cutsuch that the side walls formed by the opening are in contact with eachother or are in near contact. The slit does not have to be continuous,although it is continuous in a preferred embodiment. The slit need notbe straight but can have curvatures or angles. The contact or nearcontact of the side walls can be referred to as the normally closed orrelaxed state or position. The cross-sectional thickness of the domediminishes in the area adjacent the slit, reducing total apicaldeflection upon collapse of the slit toward the concave surface. Thedome inner surface includes an orthogonal rib that biases the wall ofthe dome adjacent the slit to a closed position, for another embodimentthe rib can be raised and elongated. Upon application of a predeterminedpressure, the slit opens toward the convex surface for facilitatingfluid flow in the intended direction. At lower pressures, the slitresumes a closed position to check fluid flow. Relatively greaterreverse pressure is required to collapse the slit toward the concavesurface to permit reverse fluid flow. The valve includes an outstandingcircumferential flange for engagement within a housing.

Objects and advantages of this invention will become apparent from thefollowing description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a combination diagrammatic and perspective, partially explodedview of a flow control valve assembly in accordance with the invention,installed in a medical fluid infusion system.

FIG. 2 is an enlarged sectional view taken along line 2-2 of FIG. 1 andshows details of the housing construction.

FIG. 3 is a front perspective view of the valve depicted in FIG. 1.

FIG. 4 is an enlarged bottom plan view of the valve depicted in FIG. 1.

FIG. 5 is an enlarged top plan view of the valve depicted in FIG. 1,showing the rib in phantom.

FIG. 6 is a further enlarged sectional view taken along line 6-6 of FIG.4 and shows details of the valve slit.

FIG. 7 is a still further enlarged sectional view taken along line 7-7of FIG. 4 and shows details of the rib.

FIG. 8 is a fragmentary sectional view similar to the view shown in FIG.2 at a reduced scale, showing the valve in an open, forward fluid flowenabling position.

FIG. 9 is similar to the view depicted in FIG. 8, showing the valve in acollapsed, reverse fluid flow enabling position.

FIG. 10 is an enlarged sectional view of a valve assembly incorporatingan alternate threaded Luer housing.

FIG. 11 is an enlarged bottom plan view of an alternate valve having acylindrical rib configuration.

FIG. 12 is an enlarged sectional view taken along line 12-12 of FIG. 11and shows details of the valve slit.

FIG. 13 is an enlarged bottom plan view of a second alternate valvehaving a cruciform rib configuration.

FIG. 14 is an enlarged sectional view taken along line 14-14 of FIG. 13and showing details of the rib.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure.

Certain terminology will be used in the following description forconvenience in reference only and will not be limiting. For example, thewords “distally” and “proximally” will refer to directions respectivelytoward and away from a patient.

Referring now to the drawings, a pressure actuated flow control valveassembly in accordance with the invention is generally indicated by thereference numeral 10 and is depicted in FIGS. 1 and 2. FIG. 1illustrates exemplary use of the valve assembly 10 installed in-linebetween an intravascular device 12 such as an intravenous (IV) fluiddelivery catheter set and an intravascular fluid source 14, such as anIV fluid reservoir. Those skilled in the art will appreciate that thepressure actuated valve assembly 10 can also be used in conjunction witha variety of other medical fluid delivery devices, such as an arterialcatheter and associated chemotherapy fluid reservoir and/or pressuremonitoring device, or a gastrostomy tube set having a correspondingfluid reservoir.

The intravascular device 12 includes an elongate, flexible catheter 16having an outer surface and an inner surface defining a lumen or fluidpassageway 18. A distal end of the catheter 16 is adapted for insertioninto a vein of a patient. The outer surface of the proximal end of thecatheter 16 is over molded by a compression strain relief cuff 20 and iscoupled with a Y-connector 22, which serves as a manifold for coupling apair of connector tubes 24 in fluidic communication with the singlecatheter 16. Each connector tube 24 has an outer surface and an innersurface defining a lumen 26, and proximal and distal end portions 28 and30 respectively. The proximal end portions 28 are each over molded by acompression strain relief cuff 32. The Y-connector 22 receives thedistal end portions 30. While FIG. 1 depicts an intravascular device 12having two connector tubes 24, it is foreseen that any operable numberof such tubes may be employed, including a single tube. In addition,while FIG. 1 depicts only the distal end of the catheter 16 asindwelling, the entire intravascular device 12 may be constructed forindwelling installation and use.

As more fully described herein, each connector tube proximal end portion28 is coupled with a valve assembly 10, which in turn is coupled with aconnector 34. The connector 34 has a generally cylindrical overall shapeand is hollow and open at one end to receive the valve assembly 10. Theconnector 34 includes a threaded interior surface 36 and an exteriorsurface 38 that is swaged or flanged to facilitate gripping. One end ofthe connector 34 is axially apertured to permit coupling with a supplytube 40 having an outer surface and an inner surface defining a fluidpassageway or lumen 42. The outer surface of the supply tube 40 adjacentthe connector 34 is equipped with a molded fitment 44 to accommodatetubing attachment. The proximal end of the supply tube 40 is coupledwith the fluid reservoir 14 so that the lumen 42 is in fluidiccommunication with the reservoir 14.

Although not shown in FIG. 1, the connector 34 may also be equipped witha stopcock or a plurality of infusion ports with plugs for receiving asyringe and/or needle. A pump may be installed in line with the supplytube 40, which may also be equipped with clamps (neither is shown).

The catheter 16, connector tubes 24 and supply tube 40 are flexible andpliant to facilitate placement, usage, and to minimize both mechanicalinsult to the blood vessels and patient discomfort during long-term use.They may be constructed of any suitable medical grade material, such as,for example, polyethylene, polyvinyl chloride, Teflon, siliconeelastomer or polyurethane or mixtures thereof. The material may becoated or impregnated with an antimicrobial or antiseptic composition toreduce bacterial adherence and biofilm formation. The catheter 16 mayalso be constructed of a radiopaque material in order to facilitateimaging for locating any breaks and/or separated sections.

The strain relief cuffs 20 and 32 and fitment 44 are constructed of anelastomeric medical grade synthetic resin material. The connector 34 maybe constructed of a medical grade rigid or semirigid synthetic resinousmaterial suitable for supporting an operable threaded connection, suchas, for example, polyvinyl chloride or polycarbonate.

As best shown in FIGS. 1 and 2, the valve assembly 10 broadly includes ahousing 46 supporting a valve member 48. The housing 46 has an elongate,stepped external configuration surrounding an internal fluid passagewayor lumen 50. The lumen 50 has an enlarged diameter adjacent the proximalend to form a hemispherical cavity 52 sized for receiving thedome-shaped valve 48. The housing 46 includes a hub portion 54, which isshown positioned for installation in a proximal orientation and a bodyportion 56 shown in a distal orientation. The housing 46 is formed of asuitable medical grade synthetic resin, such as for example, apolycarbonate.

The body 56 includes a tapered nipple 58 sized for reception within thelumen 26 of a connector tube 24. The nipple 58 includes a plurality ofspaced, radially expanded annular barbs 60. While FIG. 1 depicts twobarbs 60 evenly spaced along the nipple 58, it is foreseen that anynumber of barbs 60 may be included with any suitable degree of radialexpansion and in any spaced configuration.

The proximal end of the nipple 58 is radially expanded to form amidportion or barrel 62, having a pair of opposed axial flanges orfinger tabs 64 to facilitate manual rotation of the valve assembly 10.The barrel 62 is radially expanded at the proximal end to form anannular seat 66 for receiving the hub 54. The seat 66 includes a seriesof concentric steps 68 perpendicular to the axis of the lumen 50, eachstep 68 presenting a concentric side wall 70, which is coaxial with thelumen 50. The proximal step 68 serves as a valve seat 72. The surface ofthe valve seat 72 includes a raised annular ring or stake 74, having anangular or pointed, proximal surface adapted for gripping engagement ofa valve 48.

The hub 54 has a hollow, stepped cylindrical configuration, including adistal skirt portion 76 and a proximal neck 78 with a central lumen 80.The inner surface of the skirt includes a series of concentric steps 82,each including a concentric side wall 84 for mating engagement withrespective corresponding steps 68 and side walls 72 of the body portion56. The proximal step serves as a valve seat 86. The surface of thevalve seat 86 includes a raised annular ring 88, for gripping engagementof a valve 48. One of the steps 82 subtends an angle of less than 90 toform an energy director 90. The neck 78 includes a series of female Luerlock threads, 92 designed for mating engagement with correspondingstandard male IV Luer threads in the connector 34. Alternately, aconventional threaded or bayonet-type fitting may be substituted in theneck 78 and connector 34 for the Luer fittings shown and described.

As best shown in FIGS. 3-9, the valve member 48 includes a dome portion94 coupled with an outstanding radial flange or lip portion 96. It isalso foreseen that the flange 96 may be of lesser radial extent oromitted entirely. The valve 48 has outer and inner surfaces 98 and 100respectively and includes a circumferential slit 102 centered on thedome 94. The slit 102 extends across the fluid flow path for providingfluid communication through the valve 48 when it is in an open position.As best shown in FIGS. 3 and 5, the slit 102 is bisected by a centralaxis C, is coplanar with a slit axis 5, and is crossed by a rib axis Rperpendicular to axis S. As shown in FIG. 6, the slit 102 extendslengthwise and has outer and inner margins 104 and 106 and a pair ofends 108 and 110. Because the outer margin 104 is longer than the innermargin 106, the ends 108 and 110 subtend an angle.

As illustrated in FIGS. 6 and 7, the outer surface 98 of the valve dome94 has the symmetrical configuration of a hemisphere. It is alsoforeseen that the dome 94 may be configured as a spherical cap orchordal segment (the region of a sphere that lies above a chordal planethat does not pass through the center of the sphere) which may be eithergreater or less than one-half of a sphere. The valve dome 94 need not bestrictly hemispherical or partially spherical; however it is preferredthat it be at least dome-like or cap-like. The outer and inner surfaces98 and 100 of the valve dome 94 are not perfectly concentric. The innersurface 100 of the valve dome 94 is depicted as having a generallyhemispherical configuration, with a slightly increased curvature as itapproaches the axis C. As a result, the dome 94 has a variable wallthickness, which diminishes as it approaches an apex region of the dome94 at the axis C.

The inner surface 100 of the valve dome 94 is shown in FIGS. 4 and 6-7and in FIG. 5 in phantom to include an elongate rib 112. The rib 112extends generally circumferentially inwardly in the direction of axis R,perpendicular to and centered on the slit 102, and serves to bias theslit 102 to the closed position depicted in FIG. 3. The rib 112 is ofapproximately rectangular overall configuration, including a pair ofspaced, parallel side surfaces or sides 114 and a pair of ends 116convergent with the inner surface 100 of the valve dome 94.

As shown in FIGS. 6 and 7, the rib 112 has a depth 118 which diminishesas the ends 116 are approached. The rib 112 may be constructed so thatthe depth 118 also diminishes as the sides 114 are approached. The rib112 is bisected by the slit 102 at a center portion 120 of the rib.Thus, the wall thickness of the dome thins as it approaches thegeometric center of the slit 102, and is reinforced at the center alongaxis R by the depth of the rib 112. It is foreseen that, rather thanbisecting the rib 112, the slit 102 may intersect the rib 112eccentrically or asymmetrically, or that the slit 102 may be coextensivewith the rib 112. It is also foreseen that the ends of the rib 116 couldbe truncated (not shown) so that the depth 118 does not diminish as theends 116 are approached, or that the ends 116 could be constructed sothat the depth 118 increases as the ends are approached.

FIGS. 11 and 12 depict a valve 122 having an alternate rib construction.The structure of the valve 122 is substantially identical to thatpreviously described, and the numbering and description of like elementsand axes is hereby adopted and will not be reiterated. The valve 122includes a circumferential slit 124 centered on the dome 94. The innersurface 100 of the dome 94 includes a rib 126 having an approximatelyhemi-cylindrical overall configuration, including a curvate surface 128and a pair of ends 130 convergent with the inner surface 100 of thevalve dome 94. As previously described, the rib depth diminishes as theends 130 are approached.

FIGS. 13 and 14 depict a valve 132 having a second alternate ribconstruction. The structure of the valve 132 is also substantiallyidentical to that previously described, and the numbering anddescription of like elements and axes is also adopted and will not bereiterated. The valve 132 includes a circumferential slit 134, alsocentered on the dome 94. The inner surface 100 of the valve dome 94includes a rib 136 having an approximately X-shaped or cruciform overallconfiguration. The rib 136 has a first leg 138 and a second leg 140,each of approximately rectangular overall configuration. Each of thelegs 138 and 140 include a pair of sides 142 and 144, and a pair of ends146 and 148 respectively. The first leg 138 is coextensive with the slit134, whereas the second leg 140 is orthogonal to the slit 134. The legends 146 and 148 are convergent with the inner surface 100 of the valvedome 94. As previously described, the rib depth diminishes as the ends146 and 148 are approached. Those skilled in the art will appreciatethat, in addition to the rib configurations previously described, therib may be of oblong, elliptical, quadrilateral, star-shaped, curvate,compound curvate, circular, curvilinear or any other suitableconfiguration.

The valve dome 94, lip 96 and ribs 112, 126 and 136 are of unitaryconstruction and are formed of a resilient medical grade elastomericmaterial such as a silicone elastomer. The characteristics of thematerial used to construct the valve 48 and housing 46, the dimensionsof the valve dome 94, flange 96, ribs 112, 126 and 136 and slit 102, 124or 134 the wall thickness of the valve 48 as well as the magnitude ofthinning of the wall as it approaches the top of the dome 94 andlocation of the slit 102, 124 or 134 (whether centered on the dome oreccentric) are variables which collectively determine both the magnitudeand difference between individual pressure differentials P₁ and P₂ underwhich the slit 102, 124 or 134 flexes in forward and reversefluid-enabling manner.

The valve assembly 10 may be constructed by aligning the valve member 48or 122 or 132 on the body portion 56 of the housing 46 that the outersurface 98 of the valve flange 96 engages the body valve seat 72 andprojecting stake 74, and is received within cavity 52.

The hub 54 is installed over the body 56 with the body and hub steps 68and 82 in mating engagement and the hub valve seat 86 and projectingring 88 overlying the valve flange 96. The hub 54 and body 56 are thensubject to ultrasonic welding under pressure to form a hermetic seal.The energy director 90 serves to direct the ultrasonic melt, so that thesurfaces of the mated steps 68 and 82 fuse and the valve flange 96 iscaptured between the stake 74 and the ring 88 in a generally S-shapedcross sectional configuration as depicted in FIG. 2. In this manner, thevalve 48 or 122 or 132 is secured in place against dislodgement by fluidpressure or force exerted by any object which might be inserted into thehousing lumen 50. Alternatively, the hub 54 and body 56 may be securedtogether by an adhesive composition, by a strictly mechanical junction,or by other arrangements.

The valve assembly may be installed in an intravascular device 12 bygrasping the housing 47 and using the finger tabs 64 to rotatinglyintroduce the nipple 58 into the lumen 26 at the proximal end portion 28of a connector tube 24 until all of the barbs 60 are received within thelumen 26. The barbs 60 serve to frictionally engage the inner surface ofthe connector tube lumen 26 in a force fit. It is foreseen that, where asingle IV line is to be employed, a connector tube 24 may be unnecessaryso that the housing 46 may be introduced directly into the catheterlumen 18 at the proximal end of a catheter 16. A connector 34 is alignedover the neck 78 and rotated until the threaded interior surface 36tightly engages the threads 92 of the neck 78. More than one valveassembly 10 may be installed in-line in an intravascular device 12.

In use, the catheter 16 is inserted into a blood vessel of a patient, sothat the catheter lumen 18 is in fluidic communication with thepatient's blood. If the catheter 16 is to be centrally placed, it isthen threaded into a large central vein where it may remain indwellingfor a prolonged period of time.

An intravascular fluid source or reservoir 14 is coupled with the supplytube 40 that the supply tube lumen 42 is in fluidic communication withthe reservoir. Gravity fluid flow is initiated from the fluid source 14by any conventional means, such as by opening a stopcock or removing aclamp. Fluid flow may also be initiated by actuating a pump. Fluid fromthe reservoir 14 travels in a flow path through the supply tube 40 intothe housing lumen 50 and through the valve 48 or 122 or 132 until itcontacts the inner surface 100 of the dome.

As shown in FIG. 8, when the forward fluid flow exerts or exceeds apredetermined fluid pressure differential P₁ or cracking pressureagainst the dome inner surface 100, the slit 102 flexes distally to anopen, forward flow-enabling position. In valves 122 and 132, similarpressure conditions cause similar flexion of the respective slits 124and 134. The axial thinning of the dome 94, the shorter length of theslit inner margin 106 with respect to the slit outer margin 104, and theangle subtended by the ends of the slit 108 and 110 all cooperate tofacilitate flexing of the slit 102 or 124 or 134 at a relatively lowpressure differential, such as is provided by the force of gravity on anelevated fluid reservoir.

The slit 102 or 124 or 134 remains in an open position to permit theflow of fluid in a forward direction as long as the pressuredifferential P₁ is maintained against the dome inner surface 100. Whenthe fluid supply in the fluid reservoir 14 is exhausted, the pressuredifferential against the dome inner surface 100 falls below the crackingpressure P₁, and the rib 112, or 122 or 128 serves to bias the slit 102or 124 or 134 back into a closed, flow-blocking position, depicted inFIG. 7. The rib 112, or 122 or 128 also biases the closed slit margins104 and 106 into sealing alignment, so that there is no overlap whichmight permit leakage through the valve. The pressure differential p₁ ispreselected by design so that the slit 102 or 124 or 134 closes while afluid head remains in the supply tube 40, so that air does not enter thevalve 48 or 122 or 132.

At times, it may be necessary to permit reverse fluid flow, for exampleto withdraw a blood sample. In such instances, a syringe may be insertedinto the hub 54 and the plunger withdrawn to create a negative pressure.As shown in FIG. 9, when a predetermined fluid pressure differential P₂or collapsing pressure, is exerted or exceeded against the dome outersurface 98, the slit 102 or 124 or 134 flexes proximally to an open,reverse flow-enabling position. Flexing of the slit is accompanied byproximal collapse of a portion of the dome 94. Because of the axialthinning of the dome 94 in the region of the slit once the pressuredifferential P₂ is reached, only a limited portion of the dome flexesproximally, and the entire dome 94 does not invert into the hub lumen80. In this manner, the volume of fluid displace back in to the housinglumen 50 is minimized when the pressure falls below P₂ and the rib 112or 122 or 128 biases the slit 102 or 124 or 134 back into a closed,fluid flow blocking position depicted in FIG. 7. Advantageously, thecombination of the hemispherical shape of the dome 94, the angular endsof the slit 102, the anterior thinning of the dome 94 in the region ofthe slit 102 or 124 or 134, and the rib 112 or 122 or 128 combine toprovide a valve 48 having a relatively low cracking pressure P₁, arelatively high reflux pressure P₂ and minimal fluid displacementfollowing reverse fluid flow. This combination of features permitsforward fluid flow by gravity from a reservoir and into a patient, whileinhibiting thrombus promoting fluid back flow and minimizing refluxvolume.

The structure of an alternate valve assembly housing is illustrated inFIG. 10 and is generally indicated by the reference numeral 150. Thehousing 150 has an elongate, generally cylindrical externalconfiguration surrounding a fluid passageway or lumen 152, which widensproximally for receiving the dome-shaped valve member 48 previouslydescribed. The housing 150 includes a hub portion 154 and a body portion156.

The distal portion of the body 156 is configured as a standard Luerconnector, including a standard Luer taper 158 and standard male Luerlock threaded overmantle 160 or internally threaded collar. The proximalportion of the body 156 and distal portion of the hub 154 are matinglystepped as previously described with respect to the body 56 and hub 54.The proximal portion of the hub 154 is configured with a truncated, Luerthreaded top 162.

In use, the male Luer body 156 may be rotatingly coupled with anystandard female Luer connection, while the female Luer hub 154 may becoupled with any standard male Luer connection in order to install thevalve assembly housing 150 in-line between an intravascular fluid sourceand an indwelling catheter 16. The operation of the valve member 48within the housing 150 is substantially the same as previously describedwith respect to the valve member 48 within the housing 46.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown. Havingthus described the invention, the following is claimed as new anddesired to be secured by Letters Patent:

1. A pressure actuated flow control valve, comprising: a. a flexibleunitary valve body having a central wall with a convex surface and anopposing concave surface where said central wall defines a fluidpassageway portal; and b. a normally closed slit extending through thewall and between the convex and concave surfaces where the side walls ofthe slit are in near contact with each other in a normally closedrelaxed state and said slit extending partially along the diameter ofthe central wall.
 2. The flow control valve of claim 1, where thecentral wall is dome-shaped having a substantially spherical geometry.3. The flow control valve of claim 1, where the central wall has athickness that diminishes approaching the apical area.
 4. The flowcontrol valve of claim 1, where the opposing concave surface has araised elongated rib extending substantially perpendicular to the slit.5. The flow control valve of claim 4, where the opposing concave surfacehas a second raised elongated rib extending substantially along the lineof the slit.
 6. The flow control valve of claim 1, where the lengthwiseopposing first and second ends of the slit are angled such that thearcuate length of the slit is shorter as it penetrates the concavesurface than it is when it penetrates the convex surface.
 7. The flowcontrol valve of claim 1, where the slit lengthwise end to end is notstraight.
 8. The flow control valve of claim 1, where the central wallis constructed of material having such material characteristics and saidcentral wall and said slit being so dimensionally configured as toresist opening in response to a selected range of backflow pressureapplied to said convex surface to resist a backflow of fluid.
 9. Theflow control valve of claim 1, where the central wall is constructed ofmaterial having such material characteristics and said central wall andsaid slit being so dimensionally configured such that the normallyclosed slit opens in response to a predetermined selected range of fluidflow pressure applied to said concave surface to allow a flow of fluidwhere said slit opens toward said convex surface upon application of apredetermined selected range of fluid flow pressure to said concavesurface, enabling forward flow through the portal defined by the centralwall and said slit closes to check flow through said portal defined bythe central wall at a pressure on said concave surface less than saidpredetermined selected range of fluid flow pressure.
 10. The flowcontrol valve of claim 1, wherein: a. said slit opens toward said convexsurface upon application of a predetermined first fluid pressure to saidconcave surface, enabling forward flow through said portal defined bythe central wall; b. said slit closes to check flow through said portaldefined by the central wall at a pressure on said concave surface lessthan said first fluid pressure; c. said slit opens toward said concavesurface upon application of a predetermined second fluid pressure tosaid convex surface, enabling reverse flow through said portal definedby the central wall; d. said slit closes to check flow through saidportal defined by the central wall at a pressure on said convex surfaceless than said second fluid pressure; and e. said second fluid pressureis greater than said first fluid pressure.
 11. The flow control valve ofclaim 1, where the flexible unitary body includes an outwardly extendingperipheral flange around a base of the unitary body distal from anapical area of the central wall for engaging the flexible unitary bodyin a fluid flow passageway.